Light-emitting diode device

ABSTRACT

A light-emitting diode device includes a transparent substrate having an edge side, a peripheral region and a central region surrounded by the peripheral region; and a plurality of light-emitting diode units disposed along the peripheral region and having a first light-emitting diode unit with an edge parallel to the edge side. The central region is devoid of any light-emitting diode unit.

REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 14/513,810, filed on Oct. 14, 2014, which is acontinuation application of U.S. patent application Ser. No. 13/767,217,filed on Feb. 14, 2013, now U.S. Pat. No. 8,860,046 which claims theright of priority based on Taiwan application Serial No. 101105428,filed on Feb. 20, 2012, and the content of which are hereby incorporatedby reference in their entirety.

TECHNICAL FIELD

The disclosure relates to a light-emitting diode device with high lightextraction efficiency.

DESCRIPTION OF BACKGROUND ART

The lighting theory and structure of light-emitting diode (LED) isdifferent from that of conventional lighting source. An LED hasadvantages like low power loss, long life-time, no need for warmingtime, and fast responsive time. Moreover, it is small, shockproof,suitable for mass production, so LEDs are widely adopted in the market.For example, LEDs can be used in optical display apparatus, laserdiodes, traffic lights, data storage devices, communication devices,illumination devices, medical devices, and so on.

The conventional two dimensional array light emitting diode device 1shown as FIGS. 1A and 1B comprises a transparent substrate 10, aplurality of light-emitting diode units 12 extending along twodimensions and closely arranged and formed on the transparent substrate10. Every light-emitting diode unit 12 comprises one p-typesemiconductor layer 121, one light-emitting layer 122, and one n-typesemiconductor layer 123. Because the transparent substrate iselectrically insulating, after forming the grooves by etching betweenthe light-emitting diode units 12, each light-emitting diode unit can beinsulated to each other. Then, etching part of each light-emitting diodeunit 12 to the n-type semiconductor layer 123 and forming a firstelectrode 18 and a second electrode 16 on the exposed region of then-type semiconductor layer 123 and the p-type semiconductor 121,respectively. Furthermore, the first electrodes 18 and the secondelectrodes 16 of the plurality of the light-emitting diode units 12 areselectively connected by the conductive connecting structures 19 inorder to make the plurality of the light-emitting diode units 12 toelectrically connect in parallel or in series. Wherein, there can be airunder the conductive connecting structure 19, or an insulating layer 13can be formed on part surfaces of the epitaxial layers of thelight-emitting diode units 12 and the regions between the adjacentlight-emitting diode units 12 by chemical vapor deposition method (CVD),physical vapor deposition method (PVD), or sputtering method and so onin order to protect and electrically insulate the epitaxial layers ofthe adjacent light-emitting diode units 12. The material of theinsulating layer 13 can be aluminum oxide (Al₂O₃), silicon dioxide(SiO₂), aluminum nitride (AlN), silicon nitride (SiN_(x)), titaniumoxide (TiO₂), and the combination thereof.

However, because the height difference between the grooves 14 and thelight-emitting units 12 is large, the conductive connecting structures19 electrically connecting the light-emitting diode units 12 is easy tocause the connecting failure and to influence the yield of the device.

Besides, the aforementioned light emitting diode device 1 can furtherconstitute and connect with other devices to form a light-emittingapparatus 100. FIG. 11 illustrates a conventional light-emittingapparatus 100. As shown in FIG. 11, a light-emitting apparatus 100comprises one submount 110 comprising one circuit 101 thereon; theaforementioned light-emitting diode device 1 attached on the submount110; and an electrical connecting structure 104 electrically connectingthe first electrode pad 16′ and the second electrode pad 18′ of thefirst light-emitting diode device 1 and the circuit 101 on the leadframe 110. Wherein, the aforementioned submount 110 can be a lead frameor a large-sized mounting substrate which is advantageous for circuitdesign of the light-emitting apparatus and heat dissipating. Theaforementioned electrical connecting structure 104 can be the bondingwire or other connecting structures.

SUMMARY OF THE DISCLOSURE

In accordance with the description above, the present disclosureprovides a light-emitting diode device including a transparent substratehaving an edge side, a peripheral region and a central region surroundedby the peripheral region; and a plurality of light-emitting diode unitsdisposed along the peripheral region and having a first light-emittingdiode unit with an edge parallel to the edge side. The central region isdevoid of any light-emitting diode unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a side-view structure of a conventional twodimensional array light-emitting diode device;

FIG. 1B illustrates a top-view structure of a conventional twodimensional array light-emitting diode device;

FIG. 2A illustrates a top-view structure of a two dimensional arraylight-emitting diode device in accordance with an embodiment of thepresent application;

FIG. 2B illustrates a side-view structure of a two dimensional arraylight-emitting diode device in accordance with an embodiment of thepresent application;

FIG. 3 illustrates a top-view structure of a light-emitting diode unitin accordance with an embodiment of the present application;

FIGS. 4A-4B illustrate the top-view diagrams of two dimensional arraylight-emitting diode devices in accordance with the embodiments of thepresent application;

FIG. 5 illustrates a top-view diagram of a two dimensional arraylight-emitting diode device in accordance with another embodiment of thepresent application;

FIGS. 6A-6B illustrate the top-view diagrams of two dimensional arraylight-emitting diode devices in accordance with the embodiments of thepresent application;

FIG. 7 illustrates a comparison chart of the light-emitting efficiencyand the light-emitting power of each light-emitting diode unit inaccordance with different two dimensional array light emitting diodedevices;

FIGS. 8A-8C illustrate the top-view diagrams of two dimensional arraylight-emitting diode devices in accordance with the embodiments of thepresent application;

FIGS. 9A-9D illustrate the top-view diagrams of the single stringserially-connected light-emitting diode devices in accordance with theembodiments of the present application;

FIG. 10 illustrates a top-view diagram of a two dimensional arraylight-emitting diode device in accordance with another embodiment of thepresent application;

FIG. 11 illustrates the top-view diagram of a conventionallight-emitting apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following discloses the embodiments of the present application indetail accompanying with the drawings. First, FIGS. 2A and 2B illustratethe top-view diagram and the side-view diagram of a two dimensionalarray light-emitting diode device 2 in accordance with the firstembodiment of the present application, respectively. The two dimensionalarray light-emitting diode device 2 includes a transparent substrate 20including a first surface 201 and a bottom surface 202 opposite to thefirst surface 201. The transparent substrate 20 is not limited to becomposed of a single material and can also be composed of a plurality ofdifferent materials. For example, the transparent substrate 20 can becomposed of two substrates including a first transparent substrate and asecond transparent substrate connecting to each other (not shown). Inthe present embodiment, the material of the transparent substrate 20 issapphire. In other embodiments, the material of the transparentsubstrate 20 can also comprise inorganic material such as lithiumaluminum oxide (LiAlO₂), zinc oxide (ZnO), gallium phosphide (GaP),aluminum nitride (AlN), and glass or organic polymer material. Then, anarray including a plurality of light-emitting diode units 22 extendingtwo dimensionally on the first surface 201 of the transparent substrate20 is formed. In the present embodiment, the manufacturing methoddiscloses as the following:

First, the n-type semiconductor layer 221, the light-emitting layer 222,the p-type semiconductor layer 223 are sequentially formed on a growthsubstrate (not shown) by the traditional epitaxial growth method. In thepresent embodiment, the material of the growth substrate is galliumarsenide (GaAs). In other embodiments, the material of the growthsubstrate can also comprise germanium (Ge), indium phosphide (InP),sapphire, silicon carbide (SiC), silicon (Si), lithium aluminum oxide(LiAlO₂), zinc oxide (ZnO), gallium nitride (GaN), and aluminum nitride(AlN).

Then, a part of epitaxial layers is selectively removed by thephotolithography method, and the remained epitaxial layers form aplurality of separated light-emitting diode units 22 on the growthsubstrate as shown in FIG. 2B. The light-emitting diode units canfurther include the exposed region of the n-type semiconductor byphotolithography method, and the region can be used as the platform forthe electrode to form thereon.

In order to increase the light extraction efficiency of the wholedevice, the epitaxial layer structures of the light-emitting diode units22 can be arranged on the transparent substrate 20 by the substratetransferring method or the substrate bonding method. The light-emittingdiode units 22 can be directly bonded to the transparent substrate 20 byheating, pressurizing, or bonding the light-emitting diode units 22 andthe transparent substrate 20 with a transparent adhesive layer (notshown). The transparent adhesive layer can be an organic polymertransparent glue layer, such as polyimide, benzocyclobutene (BCB),perfluorocyclobutane (PFCB), Epoxy, Acrylic Resin, and polyethyleneterephthalate (PET) or the combination thereof; a transparent conductivemetal oxide layer, such as Indium Tin Oxide (ITO), Indium Oxide (InO),Tin Oxide (SnO), Fluoro Tin Oxide (FTO), Antimony Tin Oxide (ATO),Cadmium Tin Oxide (CTO), Aluminum Zinc Oxide (AZO), and Gallium DopedZinc Oxide (GZO) or the combination thereof; or an inorganic layer, suchas aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), aluminum nitride(AlN), silicon nitride (SiN_(x)), titanium oxide (TiO₂), and thecombination thereof.

In the present embodiment, the light-emitting diode units 22 are bondedto the transparent substrate 20 by using the benzocyclobutene (BCB)series material as the adhesive layer. In practice, the method offorming the light-emitting diode units 22 on the transparent substrate20 is not limited to this embodiment; people with ordinary skill in theart can realize that depends on the different structure properties, thelight-emitting diode units 22 can also be epitaxially formed on thetransparent substrate. Besides, with different transfer frequency, forexample, transfer twice, the structure with the p-type semiconductorlayer adjacent to the substrate, the n-type semiconductor layer on thep-type semiconductor layer, and the light-emitting layer therebetweencan also be formed.

Then, forming the insulating layer 23 on partial surfaces of theepitaxial layers of the light-emitting diode units 22 and the regionsbetween the adjacent light-emitting diode units 22 by the chemical vapordeposition method (CVD), physical vapor deposition method (PVD),sputtering method, and so on in order to protect and electricallyinsulate the epitaxial layers of the adjacent light-emitting diode units22. The material of the insulating layer 23 can be aluminum oxide(Al₂O₃), silicon dioxide (SiO₂), aluminum nitride (AlN), silicon nitride(SiN_(x)), titanium oxide (TiO₂), and the combination thereof.

Then, forming a first electrode 28 on the n-type semiconductor exposedregion of the light-emitting diode unit 22, forming a second electrode26 on the surface of the p-type semiconductor layer, and forming aconductive connecting structure 29 by the sputtering method in order toelectrically connect the light-emitting diode units 22 therebetween onthe first surface 201 of the transparent substrate. Take the embodimentfor example, forming a first electrode 28 on the n-type semiconductorlayer exposed region of the first light-emitting diode unit 22, forminga second electrode 26 on the p-type semiconductor layer 223 of theadjacent light-emitting diode unit 22, and forming a conductiveconnecting structure 29 between the two electrodes in order toelectrically connect the two adjacent light-emitting diode units inseries. The material of the conductive connecting structure 29 and theelectrodes 26, 28 can be metal such as gold (Au), silver (Ag), copper(Cu), chromium (Cr), aluminum (Al), platinum (Pt), nickel (Ni), titanium(Ti), tin (Sn), the alloy or the stacks thereof. The materials of thefirst electrode 28, the second electrode 26, and the conductiveconnecting structure 29 can be the same or different, and the structuresthereof can be made by one-step process or by multi-steps process.

In order to reduce the influence of the non-transparent metal structurefor the light extraction efficiency on the light emitting diode device2, as shown in FIG. 2A, based on different circuit designs, twoconductive connecting structures 29 are respectively formed on thesurfaces of the p-type semiconductor layer 223 of one light-emittingdiode unit 22 and the n-type semiconductor layer 221 of anotherlight-emitting diode unit 22 in the light-emitting diode units chain,and are extended to the first surface 201 of the substrate 20 uncoveredby the epitaxial layer to form a first electrode pad 26′ and a secondelectrode pad 28′. Through the two electrode pads, the device canelectrically connect to external power by wiring or soldering. Theprocess of forming the electrode pads 26′ and 28′ can proceed in thesame process with forming the electrodes 26 and 28 or in multipleprocesses. The materials of forming the electrode pads 26′ and 28′ canalso be the same with or different from the materials of the electrodes26 and 28 or the conductive connecting structure 29.

FIG. 3 illustrates the enlarged top view of the light-emitting diodeunit 22. In the present embodiment, each light-emitting diode unit 22 isa rectangle having four sides 22 a (length a), 22 b (length b), 22 c(length a), and 22 d (length b), and the circumference of thelight-emitting diode unit 22 are the total lengths of the four sides,that is, 2a+2b.

In the embodiment of the present application, the arrangement of thelight-emitting diode units in the device is proposed to enhance thelight extraction efficiency of the light emitting diode device. In theconventional two dimensional array light-emitting diode device, when twolight-emitting diode units is too close, the light emitted from thelight emitting diode unit is reabsorbed easily by the semiconductorlayers which have similar band gap (especially the light-emittinglayers) in the neighboring light-emitting diode units, and the totallight extraction efficiency of the device can be influenced. In order toreduce the reabsorption, the distance between each light-emitting diodeunits 22 is enlarged. In the present embodiment, because the band gapsof the light-emitting layers are close, the light reabsorption is moreobvious. Therefore, taking the distances between the light-emittinglayers as the reference, all the distances between the light-emittinglayers of the ten light-emitting diode units is preferred to be largerthan 35 μm. Besides, the portion of the sides neighboring with anotherlight-emitting diode unit 22 is preferably reduced. Referring to FIG.4A, when the vertical distance x between the sides of neighboringlight-emitting diode units 22 is larger than 50 μm, the chance ofreabsorption between two adjacent light-emitting diode units is lower.In that case, the two sides of the light-emitting diodes with thedistance larger than 50 μm are defined as not being near each other.This definition can be extensively applied to light-emitting diode units22 with different shapes. As shown in FIG. 4B, the circularlight-emitting diode units 22 can be arranged not near each other on thesubstrate in a two-dimensional array form in order to reduce the chanceof reabsorption between each other and to enhance the light extractionefficiency of the light-emitting diode device.

In the above embodiments, a “not-near value” α for a light-emittingdiode unit 22 is defined as the ratio of the total length of the sidesof one light-emitting diode unit 22 not near another light-emittingdiode unit to the circumference of one light-emitting diode unit 22. Asshown in FIG. 5, the ten light-emitting diode units 22 are numbered andthe not-near value α of the light-emitting diode unit 22-1 iscalculated. The sides of the light-emitting diode unit 22-1 and thelight-emitting diode unit 22-2 thereunder are connected by theconductive connecting structure 29, and the vertical distance betweenthe side 22-1 c and the side 22-2 d is smaller or equal to 50 μm, thatis, the near-each-other length of the sides 22-1 c and 22-2 d is b.Similarly, the distance between the side 22-1 d of the light-emittingdiode unit 22-1 and the side 22-3 b of the light-emitting diode unit22-3 on the left hand side thereof is smaller than 50 μm. That is, theyare also near each other, and the length is b. Besides, thecircumference of the light-emitting diode unit 22-1 is 2a+2b. In thisembodiment, the light-emitting diode unit comprises the sides with thelength 2b near other light-emitting diode units, and the total not-nearlength of the sides is (2a+2b)−2b=2a. Therefore, the not-near value α is2a/(2a+2b). The same calculation formula can be applied to thelight-emitting diode units 22 with different shapes. In that case, thesides of one light-emitting diode unit are divided into a plurality ofpoints, and the tangent line along the side of each point is given. Thevertical distance along the tangent line between each point and thenearest side of other light-emitting diode units is then calculated.After determining the distance of each point with the nearestlight-emitting diode unit, all the not-near sides are integrated, andthe integral value is the total length of the not-near sides. Thenot-near value α is the ratio of the integral value to the circumferenceof the light-emitting diode unit.

Taking FIGS. 6A and 6B for example, whether each point of thelight-emitting diode unit with irregular shape is near otherlight-emitting diode units or not can be further determined. If theshape of the light-emitting diode unit is irregular, the verticaldistance x of each point is calculated by taking each point on the sideof the light-emitting diode unit along the direction vertical to theside. When the side is a curve, a tangent line for each point on thecurve is given and the vertical distance of the point along thedirection vertical to the tangent line is calculated. In FIGS. 6A and6B, light-emitting diode unit 32-1 and light-emitting diode unit 42-1are referred to demonstrate the calculation formulas for the verticaldistances between different positions of the sides of the light-emittingdiode unit and the nearest light-emitting diode units 32-2, 32-3, 42-2,and 42-3.

In accordance with the experiment results, when the not-near value α ofthe light-emitting diode unit on the two dimensional array diode deviceis larger than 50%, the light emitting efficiency of the light-emittingdiode device 2 is 5% better than that of the conventional closelyarranged two dimensional array light-emitting diode device 3. As shownin the comparison chart of the light-emitting efficiency betweendifferent light-emitting diode devices and the light-emitting power ofeach light-emitting diode unit, when the side length a of eachlight-emitting diode unit in the light-emitting diode device 2 is 560 μmand the side length b of each light-emitting diode unit in thelight-emitting diode device 2 is 290 μm, the not-near value α is about65%. The light emitting efficiency of the light-emitting diode device 2can be 10% better than the conventional closely arranged two dimensionalarray light-emitting diode device 3.

FIGS. 8A to 8C show other embodiments of the two dimensional arraylight-emitting diode devices to fit the arrangements of thelight-emitting diode units with not-near value α larger than 50%.

Besides, in order to enhance the total light emitting efficiency of thedevice, the first surface and/or the backside surface can be roughenedby wet etching method or dry etching method so the light scatteringprobability and the light extraction probability are increased.Furthermore, viewing from the top, when the light emitting diode unit 22is disposed on the transparent substrate 20, the shortest distancebetween the position of the light emitting layer of the light emittingdiode unit 22 vertically projected on the first surface and any sidefaces is preferably larger than 20 μm in order to enhance theprobability of the light extracted from the transparent substrate 20.

Under the similar concept, the single string of serially-connected highvoltage light-emitting diode devices on the transparent substrate can beadequately arranged in a two dimensional form to increase the not-nearvalue α of each light emitting diode unit in each serially-connectedlight-emitting diode device.

FIGS. 9A to 9D illustrate different single string of serially-connectedhigh voltage light-emitting diode devices 4, 5, 6, 7, respectively. Eachserially-connected high voltage light-emitting diode device comprisesfour light emitting diode units 42, 52, 62, 72 formed on the substrate40, 50, 60, 70 by epitaxy or by bonding, respectively. Similar with thestructures mentioned above, forming the first electrodes 46, 56, 66, 76on exposed regions of the n-type semiconductor of the first lightemitting diode units 42, 52, 62, 72, respectively, extending theconductive connecting structures 49, 59, 69, 79 to another adjacentlight emitting diode units 42, 52, 62, 72, and forming the secondelectrodes 48, 58, 68, 78 on the p-type semiconductor layer of theadjacent light emitting diode unit 42 in order to electrically connecttwo adjacent light emitting diode units 42, 52, 62, 72 in series. Ineach single string of serially-connected high voltage light-emittingdiode devices 4, 5, 6, 7, two light emitting diode units 42, 52, 62, 72at the two ends in each string further comprise the first electrode pads46′, 56′, 66′, 76′, and the second electrode pads 48′, 58′, 68′, 78′,respectively, which are used to electrically connect to the externaldevice or the power source.

More than one of the single string of the serially-connected highvoltage light-emitting diode devices 4, 5, 6, 7 can be attached to asingle transparent substrate 80 to a transparent adhesive layer, and thelight-emitting diode devices 4, 5, 6, 7 can be electrically connected toeach other by the wire-bonding process or forming conductive connectingstructures 89 through the photolithography process. With adequatearrangement, it is possible to form a two dimensional array oflight-emitting diode device with a not-near value α higher than that ofthe conventional compact two dimensional array of light-emitting diodedevice in order to achieve the higher light extraction efficiency asshown in FIG. 10.

The embodiments mentioned above are used to describe the technicalthinking and the characteristic of the invention and to make the personwith ordinary skill in the art to realize the content of the inventionand to practice, which could not be used to limit the claim scope of thepresent application. Any modification or variation according to thespirit of the present application should also be covered in the claimscope of the present disclosure.

What is claimed is:
 1. A light-emitting diode device comprising: atransparent substrate having an edge side, a peripheral region and acentral region surrounded by the peripheral region; a substrate; aplurality of light-emitting diode units disposed along the peripheralregion and having a first light-emitting diode unit which is formed onthe substrate and has an edge parallel to the edge side; and an adhesivelayer formed between the substrate and the transparent substrate,wherein the central region is devoid of any light-emitting diode unit.2. The light-emitting diode device of claim 1, wherein the transparentsubstrate comprises glass or organic polymer material.
 3. Thelight-emitting diode device of claim 1, wherein the plurality oflight-emitting diode units is arranged in a closed-loop configuration.4. The light-emitting diode device of claim 1, wherein the plurality oflight-emitting diode units is electrically connected to each other inseries.
 5. The light-emitting diode device of claim 1, wherein some ofthe plurality of light-emitting diode units are commonly formed on thesubstrate.
 6. The light-emitting diode device of claim 1, wherein theadhesive layer comprises a material selected from the group consistingof polyimide, benzocyclobutene (BCB), perfluorocyclobutane (PFCB),Epoxy, Acrylic Resin, and polyethylene terephthalate (PET).
 7. Thelight-emitting diode device of claim 1, wherein the first light-emittingdiode unit has a flat side surface with the edge, and the plurality oflight-emitting diode units comprises a second light-emitting diode unitand a third light-emitting diode unit separated from the secondlight-emitting diode unit by a distance larger than four times a lengthof the edge of the first light-emitting diode unit.
 8. Thelight-emitting diode device of claim 1, wherein the plurality oflight-emitting diode units is electrically connected to each other by awire.
 9. The light-emitting diode device of claim 1, wherein thetransparent substrate has a bottom surface devoid of any light-emittingdiode unit.
 10. The light-emitting diode device of claim 1, wherein theadhesive layer is transparent to light from the plurality oflight-emitting diode units.